Manufacture of lead pencils



Jan. 14, 1941. c. R. MCKEE MANUFACTURE OF LEAD PENCILS Filed April 5, 1939 INVENTO/E Ky flwn,,p@rwrr%m Patented .i'an. 14, 1941 "UNITED STATES PATENT OFFICE MANUFACTURE LEAD PENCILS Charles B. McKee, Gowan da, N. Y., assignor to This invention relates to the manufacture of pencils of the kind in which the lead or marking material is embedded in an outer sheath which may be made of wood, paper or the like, and to which it is glued or cemented.

In the manufacture of pencils of this kind, difiiculties have been encountered in obtaining a satisfactory adhesion between the lead or marking materials and the sheath, this difilculty being l0 due mainly to the fact that the marking material is generally of a nature such that glue or other cement does not adhere satisfactorily thereto. For example, in ordinary black lead pencils, the lead or marking material is generally made of a mixture of graphite and a clay or other binder or bonding material, and also includes a greasy or oily material. Glue or other adhesives do not, of course, adhere well to greasy or oily substances.

One of the objects of this invention is to provide an improved method of treating the lead or marking material, prior to assembling the same in a sheath, in such a manner that the outer surface of the lead or marking material is modified to enable glue or other adhesive to adhere securely thereto.

Another object of this invention is to provide a method of treating marking material for lead pencils by subjecting the same to an electrolytic action, whereby the surface of the marking material is modified in such a manner as to enable the adhesive to form a secure bond between the marking material and the sheath.

A further object of this invention is to provide a process of treating pencil leads or markingmaterial electrolytically in such a manner that .the marking material forms the anode of an electrolytic cell, whereupon a change takes place at the surface of the lead or marking material which enables glue or other adhesive to bond itsel'r securely thereto. A further object is to provide a process of this kind in which the leads or marking material are subjected to an electrolytic reaction by means of which a substance is deposited on the leads which forms a better bond with an adhesive than the untreated surfaces of the leads.

It is also an object of this invention to provide an improved lead or marking material which has a surface to which an adhesive can securely bond itself. A further object is to improve the manufacture of lead pencils in such a manner that the leads are securely bonded to their sheaths. I

It is also an object of this invention to provide process may be carried out.

Further objects of this invention will appear from the following description and claims.

In the accompanying drawing, I have illus- 5 trated by way-of example, two types of apparatus by means of which leads or marking material may be treated in accordance with my invention.

In the drawing:

Fig. 1 shows diagrammatically one form of 10 electrolytic cell and the electrical connections thereto, by means of which my invention may be carried out.

Fig. 2 is a diagrammatic view of a difl'erent type of apparatus for carrying out my improved 1 process.

Fig. 3 is a perspective view partly in section and partly broken away, of a pencil embodying my invention.

I have found that if the leads or other mark- 20 ing material are subjected to an electrolytic action in such a manner that the leads form one of the electrodes of an electrolytic cell, certain reactions take place which modify the surfaces of the leads in such a manner that an adhesive 25 will readily bond itself or adhere to the leads and will enable these leads to be securely bonded to the sheaths of the pencils. Consequently, in each pencil, the lead and sheath reinforce each other to resist breaking of the lead within the 30 sheath. When the leads form the anode of an electrolytic cell, the electrolyte of which preferably consists mainly of water, no material is generally deposited on the leads, but the electrolytic action, nevertheless, modifies the surfaces of 35 the leads so that glue or other adhesive will adhere securely thereto. I have, for example, obtained very good results by using ordinary tap water as the electrolyte, the usual hardness ingredients in the water being sufficient to cause 0 current to flow readily through the water. Any of the well known materials which have the property of increasing the conductivity of water may be added to water to form an aqueous solution of better current conductivity, but preferably only 4 such materials should be added to the electrolyte an improved apparatus by means of which my' as have no injurious eifects upon the leads, either while in solution or when broken up by electrolysisJ It is, for example, particularly desirable to provide an electrolyte in which no material is 50 contained which is destructive of the clay bond employed in the leads, since adhesives generally adhere better to a clay than to graphite. For example, materials which have been found particularly satisfactory for this purpose are sodium 55 bicarbonate, sodium nitrate, and sodium silicate, formaldehyde, formic acid, or other organic acids.

Strong mineral acids which attack the clay bonding material in the leads should, of course, be

avoided, as well as salts which might during elec troiysis form inorganic acids at an electrode.

Sodium bicarbonate has been found particularly suitable for use in the electrolyte, inwhich case, carbon dioxide is liberated at the'anode, together with oxygen. These gases appear to'have a very effective, action on the leads without damaging the clay bond. The oxygen liberated at the anode appears to attack the graphite" of the leads, as well as the greasy material or lubricant and dition for'bonding with an adhesive, 4

leaves the surfacesof the leads' in excellent con- After treatment of the leads in an electrolytic cell for a short period of time, it will-be noted that when they are removed from -theelectrolytic cell, the surfaces of the leads appeardark in color and have lost the luster which isprobably produced by the greasy or oily material on the sur-z faces of the leads. When tap-water or other electrolytes are used, which do not cause any deposit of solid material on the surfaces of the leads, these leads are then immediately ready to It is be assembled or cemented to the sheaths. also preferable to have the leads assembled fairly promptly after the electrolytic treatment, since if this assembly or cementing is delayed for several hours or more, the greasy material in the leads seems to exude or work outwardly toward the surface, and thusinterferes with the satisfactory adhesion between the leads and the adhesive. It is also desirable to avoid as much as possible the handling of the leads between the time that they are treated electrolytically and their assembly in the pencils, since the handling or rubbing of the surface appears to break down the surface structure which results in superior adhesion.

While I do not know definitely all of the reasons why better adhesion is obtained when the leads are treated in accordance with my process, it seems likely that the treatment of the leads at the anodes of an electrolytic cell may cause the loose graphite plates or flakes on the surfaces of the leads to be removed, or to extend outwardly from these surfaces, resulting in a rougher surface which can be adheslvely bonded with glue to the sheath. It may also be that the electrolytic treatment exposes the outer particles of clay bonding material on the surfaces of the leads. Glue'and other adhesives will, of course, adhere well to such clay bonding material. It is also probable that the electrolytic action improves the adhesion for the reason that the oily or greasy material is removed entirely or in part from the outer surfaces of the leads, possibly by corrosion or by disturbance of the graphite beneath it, or because the graphite particles in the leads are etched or modified by oxygen collecting on the leads during the electrolytic reaction, thus producing a roughened surface of the graphite particles to which the adhesive or cement may securely bond itself. Regardless ofwhat the reasons may be for securing the improved bond, I have found that after treatment by my process, the leads may be very securely glued or cemented to their sheaths throughout their lengths, even though the same glue or adhesive is employed, which, without my improved process, results in very defective bonds between the leads and their sheaths.

The extent to which the leads are subiected to by treating the leads electrolytically in such a manner that the leads form the cathode of the the leads, any suitable material being usable for that purpose, such for example as magnesium, calcium and copper compounds. In that case,

slightly acid, for example, by the addition thereto have, for example, been obtained by treating seven leads at the anode of the electrolytic cell for twenty minutes with a current of one-half 5 ampere at'about fifty volts. I have also found that with. a materially increased current density,

the duration or treatment of the leads may be reduced totwo minute's or. less. Longer or more continued treatmentdoes not materially improve the-fladhesion, although itfdoes not harm the leads nor-their adhesion to their sheaths.

In case the electrolyte contains silicates or similar negative depositing materials, it is advisable to-"di p"the treated leads in an approximately 1% acid solution to neutralize the electric charge stored on the leads when they are removed from the electrolytic cell.

Very satisfactory results can also be obtained electrolytic cell. When this is done, the electrolyte should contain some material which can be electrolytically deposited on the. surface of slight coatings are deposited on the surfaces of the leads, to which adhesive will securely bond itself and whichcoating is in turn bonded to the lead or marking material.

I have also found that when the leads are treated at thecathode of an electrolytic cell, it is preferable to use a wetting agent with the glue employed for securing the sheaths to the leads. Any suitable wetting agent, such for example as a sulphonated oil maybe employed for this purpose. I

I have also found that if the leads are treated in an electrolytic cell as described, they take on electric charges. Glue may be electro-positive or electro-negative, depending upon whether the same is slightly acid or slightly alkaline in reaction. If the glue has an electric charge opposite to that of the lead, a greatly improved adhesion results because of the attraction of glue to the oppositely charged lead. If, as a result of the electrolytic treatment, the leads retain electro-negative charges, the glue may be made 60 of small quantities of lactic acid or other acid not injurious to the glue or to the materials on which the glue is used. Glue which is charged electronegatively can be used to advantage when the leads contain electro-positive charges.

It will be obvious from the foregoing that the leads may be treated in any suitable or desired type of electrolytic cell and by way of example, I have shown in Fig. 1, more or less diagrammatically, a cell which may be used for this purpose. This cell may include a container 5, preferably of non-conducting material and containing an electrolyte or bath 8. -|.represents the leads or marking material, which in the construction shown, are held at one end in a suitable clamp or holder I which may be supported on the container I in any suitable manner, for example, by means of brackets I.

The electric current may, of course, be obtained from any suitable source, a motor generator set being shown in Fig. 1, comprising a motor ll connected to a direct current generator II. The I positive brush or terminal of the generator is connected by means of a conductor 14 to the holder 8 in any suitable manner, and another is conductor l leading from the negative brush or terminal of the generator may be suitably connected with a cathode l6, which may, for example, be a part of the wire of the conductor It 5 itself, or a plate, if an increased area of thecathode is desired. If'will be obvious that in this cell, current enters the electrolyte through the leads I and passes through the electrolyte to the cathode It. The substance liberated at the an- ID ode produces the desired effect upon the leads. A relatively small amount of current is sufiicient to produce the desired effect, approximately one and one-half ampere minutes per lead of ordinary size being suiiicient.

It will, of course, be obvious that the same cell shown in Fig. 1 may be used, if the leads are to be treated at the cathode of the cell, and this could be accomplished by simply connecting the conductor I! with the positive terminal or brush of the generator and the conductor It with the negative terminal thereof.

In Fig. 2, I have shown a modified form of apparatus by means of which a relatively large number of leads may be conveniently treated at one time without separate handling of the same. In this case, I provide a tumbler 20 preferably arranged in inclined position. The tumbler may, for example, have'a shaft 2| secured thereto, by means of which the tumbler 20 may be ro- 80 tated about its axis; The shaft 2| may, for example, be iournalled in suitable bearings 22 and 23 supported from a base 24, and if desired, the tumbler itself may be supported from this base by means of rollers 25. The shaft 2| may be slowly rotated in any suitable manner, for example, by means-of a worm 28, which drives a worm wheel 23 fixed on the shaft 2|. Y

The leads may be deposited, in the tumbler so that they extend substantially parallel to the axis of rotation of the tumbler and as the tumbler revolves, the leads "will also rotate in such a manner as to expose different portions of their surfaces to electrolytic action. The tumbler 20 contains a solution or electrolyte 30 and the oathode 3| may dip into the solution. This cathode is connected'in the construction shown by means of the conductor 32 with the negative terminal of a source of electric current, such as a generator 33 which may, for example, be driven by a motor 35. The positive terminal of the generator is connected by means of a conductor 36 to the tumbler 20 or a part electrically connected therewith. For example, the conductor 36 may connect with a suitable brush 3! contacting with a cylindrical surface 38'formed on the shaft 2|, which shaft is, of course, connected with the tumbler 20 in such a manner that current will be conducted through the shaft to the tumbler.

If desired for convenience in handling, a removable liner or basket may be provided within the tumbler so as to facilitate the placing of leads into the tumbler and removal of the same from the tumbler. In the construction shown for this purpose, I have provided a basket 43,

having a cylindrical portion 4| which is preferably perforated, and in which the leads may be contained. The basket may, consequently, be readily removed from the tumbler by first removing the electrode 3|.

In this construction, the current passes from the generator through the conductor 36 and shaft 2| to the tumbler 20 and is conducted to the leads. The current then passes through the electrolyte to the cathode 3|. This cathode is, of course,

shown in the accompanying drawings merely diagrammatically in the form of a wire extending into the electrolyte into proximity to the leads, but the cathode may be of any suitable shape or form such that the'current from the tumbler to the cathode will pass through the leads to the 6 electrolyte in preference to passing directly from the tumbler to the electrolyte, and in the construction shown, the portion of the, wire extending into the tumbler and forming the cathode 3| is shown bent in a directon to extend 10 into proximity to the leads I. My other means for assuring the passage of the greater portion of the current through the leads may be employed, if desired.

If it is desired to treat the leads in such man- 1 nor that the same form the cathode of the electrolytic cell, this can readily be accomplished as desired in connection with Fig. 1, by reversing the connections of the conductors l2 and 38 at the generator 33.

It will of course,be obvious that the foregoing description for my improved process is applicable only to leads or marking materials of the kind which are capable of conducting electricity and which are not soluble in water, and the term 25 lead, as herein used, is intended to designate any marking material for pencils which is a conductor of electricity and which is relatively insoluble in water or in aqueous solutions used as electrolytes. My improved process,,however, is 30 very efiective with any form of current conducting and water insoluble leads or marking materials.

Because of the slow rotation of the drum 20. the leads positioned therein will roll in contact 35 with each other so that the surfaces of all of the leads will be substantially uniformly acted upon by the electric current.

In Fig. 3, I have shown one of my improved leads I incorporated in a pencil by gluing the 40 lead in the semi-circular grooves formed in the two halves 48 of the sheath. The same adhesive which secures the two halves of the sheath together also bonds the lead treated, as herein described, securely to the sheath. 45

I claim as my invention:

1. A method of treating a pencil lead before incorporating'the same in a sheath, which comprises arranging the lead to form an electrode in an electrolytic cell containing an electrolyte 50 which is substantially free from metallic compounds of the type which during electrolysis form a metallic deposit on an electrode, and passing an electric current through said lead and said cell to modify the surface of said lead to 55 enable the same to be securely bonded adhesively to an enclosing sheath.

2. A method of treating .a pencil lead before incorporating the same in a sheath, which comprises arranging the lead in an, electrolytic cell 60 to form the anode thereof, said cell containing an electrolyte free from material which is injurious to the lead, and passing an electric current into said cell through said lead, to modify the surfaces of said lead to enable the same to be securely bonded adhesively to an enclosing sheath.

3. A method of treating a pencil lead before incorporating the same in a sheath, which com- 70 prises passing an electric current through the lead while the same constitutes an electrode of an electrolytic cell containing an electrolyte consisting substantially entirely of water and free from material which is injurious to the lead, 75

toformontheleadasurfacetowhichanadhesive may be securely bonded.

4. A method of treating a pencil lead before incorporating the same in a sheath, which comprises arranging the lead in an electrolytic cell containing an electrolyte comprising mainly water and free from material which is injurious to the lead, in such a manner that the lead forms the anode of said cell, to roughen the surface of said lead to enable the same to be securely bonded to an adhesive.

5. A method of treating pencil leads, which comprises arranging a lead in an electrolytic cell containing an electrolyte comprising mainly water and free from material which is injurious to the lead, passing an electric current into said cell through said lead with said lead forming the anode of said cell, and acting on the surface of said lead with nascent ongen while in said cell to modify the surface of said lead to enable the same to be securely bonded to a sheath by means of an adhesive.

6. A process of manufacturing lead'pencils, which comprises arranging a lead in an electrolytic cell to form an electrode thereof, said cell containing an electrolyte free from material which is injurious to the lead, passing an electric current through said cell and said lead to modify the surface thereof for better bonding with an adhesive, and securing said lead by means of an adhesive to a sheath before grease from the interior of said lead exudes to the surface thereof.

7. A process of manufacturing lead pencils, which comprises arranging a lead in an electrolytic cell, containing an electrolyte comprising mainly water and free from material which is injurious to the lead, passing an electric current through said cell with said lead forming-the anode of said cell, to modify the surface of said lead and remove greasy material from the same, andsecuringsaidleadbymeansof anadhesive to a sheath before grease from the interior of said lead exudes to the surface thereof.

8. A method of making pencils, which includes subjecting the lead of the pencil to an electrolytic action in an electrolytic cell which contains an electrolyte free from material injurious to the leads, and in which the lead forms an electrode, to impart to the lead an electric charge, adjusting the pH value of glue to impart to the glue an electric charge of the opposite polarity as that of the lead, and then applying the glue to said lead and to a pencil sheath before grease from the interior of the lead exudes to the surface thereof to form a secure bond between said lead and to form a secure bond with an adhesive.

9. A pencil including a sheath and a lead secured to said sheath by an adhesive, the lead having a surface which has been treated electrolytically to form a secure bond with an adhesive.

10. A pencil lead having its outer surface roughened by treating the lead electrolytically at the anode of an electrolytic cell, to produce a surface capable of forming a secure bond with an adhesive.

.11. A lead pencil including a lead having a layer of material electrolytically deposited on the surface thereof: and capable of forming a secure bond with an adhesive, and a sheath about said lead and secured therto by an adhesive.

12. A pencil including a lead securely bonded by an adhesive to a sheath and characterized in that the lead has its outer surface etched by electrolytic action while forming the anode of an electrolytic cell.

13. A pencil including a lead securely bonded by an adhesive to a sheath and characterized in that the lead has a layer of a substance deposited on the outer surface thereof while forming the cathode of an electrolytic cell, said layer forming a secure bond with an adhesive.

14. A method of treating pencil leads before incorporating the same in a sheath, which comprises moving a plurality of said leads in the electrolyte of an electrolytic cell while supported on a current conducting member, connecting said member' in an electric circuit including said electrolyte and said leads, and continuing the passage of electric current through said electrolyte and said leads for a sufficient interval of time to modify the surfaces of said leads to enable an adhesive to bond itself securely thereto, said leads constituting an electrode of said cell.

CHARLES R. McKEE. 

